We report the implementation of projective measurement on a single 1/2 nuclear spin of the (171)Yb atom by measuring the polarization of cavity-enhanced fluorescence. To obtain cavity-enhanced fluorescence having a nuclear-spin-dependent polarization, we construct a two-mode cavity QED system, in which two cyclic transitions are independently coupled to each of the orthogonally polarized cavity modes, by manipulating the energy level of (171)Yb. This system can associate the nuclear spin degrees of freedom with the polarization of photons, which will facilitate the development of hybrid quantum systems.
We have investigated the dynamical entanglement and quantum steering in a pulsed hybrid opto-electro-mechanical system. Using the symmetric and asymmetric criteria, the possibilities of bipartite entanglement, one-way steering, two-way steering, and collective tripartite steering have been studied between different output modes. In addition, the influence of the squeezing parameter on the amount of tripartite steering measurement is also examined. The results show that a higher electro-mechanical coupling rate leads to stronger tripartite steering. The microwave cavity mode can enhance the output quantum steering and remotely steers the optical cavity. Thus, the slower mode can steer the faster mode. Such hybrid systems can serve as frequency converters between microwave and optical domains and can have a profound impact on building quantum networks of microwave-operated superconducting quantum computers.
Quantum phase transitions in spin systems are supposed to be accompanied by a soft collective mode, which has not been seen in experiments. Here, we directly measure the low energy excitation modes of a well-known realization of the Ising model in transverse field, LiHoF
4, using microwave spectroscopy techniques to probe energies well below what is accessible via neutron scattering experiments. Instead of the single excitation expected for a simple quantum Ising system, we find and characterize a remarkable array of `electronuclear' modes, arising from coupling of the spin-1/2 Ising electronic spins to a bath of spin-7/2 Ho nuclear spins. The lowest-lying electronuclear mode softens at the approach to the quantum critical point from below and above, a softening that can be quenched with the application of a longitudinal magnetic field. The electronuclear mode structure has direct implications for the Ising systems that serve as the building blocks of adiabatic quantum computers and quantum annealers.